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CONTENTS
Volume 9, Number 1, January 2012
 

Abstract
The size-effect study of various fracture parameters obtained from two parameter fracture model, effective crack model, double-K fracture model and double-G fracture model is presented in the paper. Fictitious crack model (FCM) for three-point bend test geometry for cracked concrete beam of laboratory size range 100-400 mm is developed and the different fracture parameters from size effect model, effective crack model, double-K fracture model and double-G fracture model are evaluated using the input data obtained from FCM. In addition, the fracture parameters of two parameter fracture model are obtained using the mathematical coefficients available in literature. From the study it is concluded that the fracture parameters obtained from various nonlinear fracture models including the double-K and double-G fracture models are influenced by the specimen size. These fracture parameters maintain some definite interrelationship depending upon the specimen size and relative size of initial notch length.

Key Words
concrete fracture; fracture process zone; cohesive stress distribution; nonlinear fracture models; size-effect; three-point bending test.

Address
Shailendra Kumar: Department of Civil Engineering, National Institute of Technology, Jamshedpur-831 014, India; Department of Civil Engineering, Indian Institute of Technology, Kharagpur-721 302, India
S.V. Barai: Department of Civil Engineering, Indian Institute of Technology, Kharagpur-721 302, India

Abstract
This paper presents the numerical simulation of the rigid 12.6 mm diameter kinetic energy ogive-nosed projectile impact on plain and fiber reinforced concrete (FRC) targets with compressive strengths from 45 to 235 MPa, using a three-dimensional finite element code LS-DYNA. A combined dynamic constitutive model, describing the compressive and tensile damage of concrete, is implemented. A modified Johnson_Holmquist_Cook (MJHC) constitutive relationship and damage model are incorporated to simulate the concrete behavior under compression. A tensile damage model is added to the MJHC model to analyze the dynamic fracture behavior of concrete in tension, due to blast loading. As a consequence, the impact damage in targets made of plain and fiber reinforced concrete with same matrix material under same impact velocities (650 m/s) are obtained. Moreover, the damage distribution of concrete after penetration is procured to compare with the experimental results. Numerical simulations provide a reasonable prediction on concrete damage in both compression and tension.

Key Words
concrete; material model; numerical simulation; projectile penetration.

Address
Gang Lu: Shaw Stone & Webster Nuclear, Stoughton, MA, USA 02072
Xibing Li: School of Resources and Safety Engineering, Central South University, Changsha, China 410083
Kejin Wang: National Concrete Pavement Center, Iowa State University, Ames, IA, USA 50010

Abstract
The 2D representative volume element (RVE) for softening quasi-brittle materials like concrete is determined. Two alternative methods are presented to determine a size of RVE in concrete subjected to uniaxial tension by taking into account strain localization. Concrete is described as a heterogeneous threephase material composed of aggregate, cement matrix and bond. The plane strain FE calculations of strain localization at meso-scale are carried out with an isotropic damage model with non-local softening.

Key Words
characteristic length; concrete; heterogeneous material; representative volume element (RVE); damage mechanics; softening; strain localization.

Address
L. Skarzynski and J. Tejchman : Faculty of Civil and Environmental Engineering, Gdansk University of Technology, Gdansk, Poland

Abstract
According to the results of three-point bending tests of rubberized concrete and plain concrete, the parameters such as total fracture energy (GF), initial fracture energy (Gf), and tensile strength (ft) are obtained for concrete material. Using ABAQUS software and a bilinear softening fictitious crack model, the crack propagation process was simulated and compared to the experimental results. It is found that the increase of AE hit count has a similar trend with the increase of energy dissipation in FEM simulation. For two types of concretes, both experimental results and numerical simulation indicate that the rubberized concrete has a better fracture resistance.

Key Words
concrete; fracture; acoustic emission; fictitious model.

Address
Chao Wang: School of mechanics and materials, Hohai University, Nanjing, China 210098; Jiangsu Key Laboratory of Construction Materials, Southeast University, Nanjing, China, 211189

Yamei Zhang and Zhe Zhao: Jiangsu Key Laboratory of Construction Materials, Southeast University, Nanjing, China, 211189

Abstract
The purpose of this study is to evaluate the behavior and strength of prestressed concrete deep beams using nonlinear analysis. By using a sophisticated nonlinear finite element analysis program, the accuracy and objectivity of the assessment process can be enhanced. A computer program, the RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), was used for the analysis of reinforced concrete structures. Tensile, compressive and shear models of cracked concrete and models of reinforcing and prestressing steel were used to account for the material nonlinearity of prestressed concrete. The smeared crack approach was incorporated. A bonded or unbonded prestressing bar element is used based on the finite element method, which can represent the interaction between the prestressing bars and concrete of a prestressed concrete member. The proposed numerical method for the evaluation of behavior and strength of prestressed concrete deep beams is verified by comparing its results with reliable experimental results.

Key Words
prestressed concrete; deep beams; nonlinear analysis; material nonlinearity; bonded or unbonded prestressing bar element.

Address
T.H. Kim: Construction Technology R&D Center, Samsung C&T Corporation, 1321-20 Seocho2-dong, Seocho-gu, Seoul 137-956, Korea
J.H. Cheon and H.M. Shin: Department of Civil and Environmental Engineering, Sungkyunkwan University,
300 Cheoncheon-dong, Jangan-gu, Suwon-si, Gyeonggi-do 440-746, Korea


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